Effects of mineral admixtures and steel fiber on rheology, strength, and chloride ion penetration resistance characteristics of wet-mix shotcrete mixtures containing crushed aggregates

- Effects of admixtures on rheology, strength, and chloride permeability of WMS mixtures were assessed.
- Silica fume and metakaolin may improve pumpability and shootability of WMS mixtures.
- GGBFS replacements had non-significant effects on both pumpability and shootability.
- Fly ash and steel fiber increased torque viscosity, which may adversely affect pumpability.

This study presents the effects of various mineral admixtures such as silica fume, fly ash, ground granulated blast furnace slag (GGBFS), and metakaolin and steel fiber on the rheology, strength, and chloride ion penetration resistance characteristics wet-mix shotcrete (WMS) mixtures made with crushed aggregates. The mixtures tested in this study are mostly ternary mixtures blended with silica fume. Potential implications of measured rheological properties in relation to pumping and shooting performance of WMS mixtures were also analyzed. The results have shown that silica fume may be an effective admixture benefiting both pumpability and shootability of WMS. Fly ash was found to adversely affect the pumpability of WMS mixtures by markedly increasing the torque viscosity. GGBFS had non-significant effects on both pumpability and shootability, whereas it strongly improved the chloride ion penetration resistance and strength of WMS. It was also identified that no more than 5% metakaolin by mass of cement is necessary to enhance the pumpability, shootability, and chloride penetration resistance of WMS. Despite many expected advantages of using steel fibers in WMS, special attention should be paid to prevent excessive degradation of pumpability and chloride ion penetration resistance when a high dosage (>50 kg/m3) of steel fibers is used.